Berlin Environmental Atlas

04.10 Climate Model Berlin - Analysis Maps (Edition 2016)

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Map 04.10.6 Mean Number of Meteorological Climatic Parameters

General comments

With the knowledge of the climatic parameters at a reference location, the frequencies can be estimated at other places with the help of the present temperature difference. Based on the simulated air temperatures during the day and in the night at the measurement location of Tempelhof (reference time period 2001 to 2010), the difference from the mean temperature for each ISU5 block (partial) area was determined and the frequency of climatic parameters per day was determined (see Methodology / Supplementary Notes).

The number of Hot Days represents a subset of the Summer Days and is hence included in the map of days with ≥ 25 °C.
The frequency within the settlement areas depends on their structural density and their green portion. In doing so, mainly the blocks with corresponding degree of building and less green portion, such as core areas or uses similar to core areas, commercial and industrial areas with dense building or large-area sealing as well as similar area types of residential buildings show the highest values on the summer as well as Hot Days. Similar high values are shown by large settlements and high-rise buildings owing to the high share of open areas with grass, which can get strongly heated up during the day. These are contrasted by green settlement types with a strongly pronounced tree stock e.g. in Charlottenburg-Wilmersdorf with much less number of summer and Hot Days.

Even the green and open spaces show a high range, whereby a high number of summer and Hot Days per block is present over the arable land and grass lands because of the more intensive solar irradiation. Because of the micro-climate, the frequency is the lowest within the forest areas.

In case of the nightly lowest temperatures and hence also the number of Tropical Nights, the effect of the development present and hence the urban heat island effect becomes clearly apparent in the block areas. Most of the Tropical Nights can thus be seen in City East and parts of City West. These are contrasted by the green settlement types or the development near the outskirts of the city having a low number. The remaining development takes an average position in its night temperature level and hence in the number of Tropical Nights.
Owing to a strong nightly cooling, the arable land and grass lands show a low number of Tropical Nights. This is a bit more highly pronounced in case of forest areas and somewhat similar to the well green settlement areas, such as villa construction, as far as the number is concerned.

Karte 04.10.07 Climate Analysis Map

General comments

The Climate Analysis Map maps the actual state of the climate relevant for planning. To do this, the extent of the urban over-heating, the compensation effects of areas producing cold air as well as the spatial relationships between compensation and effective areas are shown. The effects of open spaces of the surrounding regions on the city area are also included.

The differentiation of spatial units "settlement area" and "green and open areas" follows a system, which derives from the area types of the Urban and Environmental Information System (ISU) (SenStadt 2010). More detailed information for deriving these spatial units is given in the accompanying text for planning advice map urban climate (Download SenStadt 2016). Figure 11 represents the spatial distribution over the city area.

Fig. 11: Complete urban distribution of the spatial units of the climate model on the basis of area types of the Urban and Environmental Information System (ISU) (SenStadt 2010)

Green and open spaces

Open spaces with vegetation having a noteworthy cold air production represent the climate and emission ecological compensation areas. A high long-wave nightly radiation during the low-exchange high pressure weather situations leads to a strong cooling of the ground-level air layer. The quantity of the cold air produced depends upon the prevalent vegetation type, the ground attributes and the related nightly cooling rate.

The total area of the potential cold-air producing green areas within the urban area is approx. 351km², which is the same as an area portion of around 39.5 % of the complete urban area and can be considered as high. In doing so, the characterisation of cold air supply within the green areas is mostly differentiated spatially. Often, the central inner-city green areas show a rather low Cold Air Volume Flow as compared to the one present at the development of the adjacent partial areas. The reason for this is that, driven by the temperature difference between the open space and construction, the cold air must first be accelerated and then the values increase in the direction of construction. In the transition area between green area and construction, the temperature gradient and hence also the intensity of the air exchange are the highest. Areas with a volume flow of > 90 m³/s are, therefore, highlighted as areas with high and very high air exchange (see Table 2). Partly, these areas also continue as areas with valorisation "Cold air activity area in settlement space" in the constructed areas.

Large, linearly shaped open areas with relatively low surface friction function as air-stream channels for cold-air transportation. In this regard, three areas of the Havel and Spree Valleys are significant. First, the Havel section between Pichel Lake and Ruhlebener Straße which conducts cold air toward the borough of Spandau along an approx. 3 km corridor; second, Rummelsburg Lake, a part of the Spree, stands out as an area through which cold air streams from old Treptow and from the Plänterwald woods toward Rummelsburg; and finally, a section of the Dahme should be mentioned, along the Grünauer Straße-Regattastraße corridor. These results coincide with the results of a report of the German Meteorological Service (DWD 1996).

However, due to the hardly distinctive orography, such relief-determined ventilation lanes are rather rare. An essential contribution to the transportation of cold air from the countryside surrounding Berlin into the urban area cannot be ascertained; rather, only some parts of the river valleys within the urban area function as air-stream channels.

Settlement areas

As already described in the Section Method (cf. Table 1), the night heat island effect has been determined 2 m above ground with the help of the statistical method of Z-transformation of the modelled night air temperature. With this method, a spatial sub-division of the settlement area can be done according to the criteria of the nightly over-heating as compared to open space conditions. In the scope of determining the areas with bio-climatic load during the night in the planning advice map, similarly, the distribution of the air temperature was included (SenStadt 2016).

Mainly the areas classified as "Heat island effect not present or weak" are more or less under the positive influence of a cold air effective area and are, in these cases, mostly marked by an adequate aeration, whose range in the construction depends on one hand on the cold air productivity (in the construction itself too), and on the other also on the obstacle effect of the respective construction type. Mainly in the densely built quarters, the blocks present in the influence area of cold-air producing areas can also be evaluated as areas with moderate to strong heat island effect in the night hours. These local phenomena indicate that in these cases the effect of the supplied cold air does not suffice to induce a clear reduction of the Air Temperature.
These are contrasted by settlement areas with a high degree of greenery, which show only a weak or no nightly over-heating. Constructed area with function relevant for climate show an open settlement structure with a total degree of sealing of less than 30 % as well as no or at the most low over-heating; they thus contribute potentially to local origin of cold air. The concrete local effect, however, depends on the respective local situation i.e. essentially on the vegetation present. Typical area types are the ones of individual, town and double houses, or, in general, the construction with garden and surrounding greenery. They often border at the cold air producing green areas and thus contribute towards aeration of further remote settlement areas having a nightly overheating.

Air exchange

Structures, which enable the air exchange and introduce cold air, are the central connecting link between compensation areas and effective areas with bio-climatic load. Pathways should generally sow a low surface roughness, whereby wood-less valley and meadow areas, larger green areas (mainly with their open areas having low vegetation) and rail lands are considered as suitable structures. Wide roads can serve only for climate compensation owing to their emission load, but not for introducing unloaded air. The pathways are subdivided in the Climate Analysis Map with respect to the process sequence. In the 'ideal case', an area producing cold air also represents a part area of a pathway.

There is a predominance of mainly thermally induced pathway types with a compensation flow purely caused by the usage dependent temperature differences. The small garden complex at Priesterweg can be mentioned as an example of such flow areas inside the city, which transport cold air from the cemetery at the Bergstraße in Steglitz as well as from islander to the north direction. The situation is similar with respect to the small park complexes at Heckerdamm as well as the public park Rehberge; here, a part of the cold air produced at the airport Tegel is forwarded towards the city interior.

On the whole, the recognised thermally induced pathways are concentrated in the following areas:

  • to the north of the line Tegel - Lichtenberg
  • to the west of the castle grounds Charlottenburg till the city limits in Staaken; partly, the cold air is introduced from the northern Gatower field as well as from the surrounding regions
  • in the south to the east of city limit to Groß-Ziethen in the city areas of Rudow and Bohnsdorf.

Areas in the direct neighbourhood of greenery/construction are not indicated as part of a pathway.

Mainly orographically induced pathways are concentrated in the eastern area of the city. These are mainly valley areas like the Wuhle and the Mühlenfließ, which function as pathways owing to their alignment, width and surface condition. To this effect, the depression line Hundekehlsee - Dianasee - Koenigssee - Halensee, originating from Grunewald can be arranged in the western part of the city.

The low lands of the larger flowing waters like Spree and Havel go beyond this function and possess, in addition, an attribute as higher-level air and ventilation pathways. The favour the air exchange in the adjacent construction even in case of stronger, higher-level weather conditions.

An extensive cold air outflow is restricted on areas with slope inclination > 1 ° and occurs rather rarely in the city area of Berlin because of the comparatively lower height differences. For this reason, this process is connected with few areas having a noteworthy slope inclination, such as those of Grunewald and the Körpernicker Bürgerheide. Furthermore, an individual cold air outflow can be assumed to the north of Tegel lake, in Kaulsdorf as well as in Forst Düppel. The cold air supply is above-average high on these sloped forest areas, since the radiation and hence the primary cooling takes place mainly from the upper crown area and not from the immediate ground vicinity. Because of the large, radiating surface of the area, the cold air also flows in and above the crown area, instead of sinking first in the area below the canopy. (Groß, G. 1989).

Other identifications

The air-hygiene situation in the main roads network is mapped via the index of air load on the basis of nitrogen dioxide (NO2) and fine dust (PM10) (SenStadtUm 2011). The spatial distribution of the load situation closely depends on the traffic volume as well as on the construction available along the road sections. The latter influences the dilution and the removal of air-hygiene air masses so that a high load is encountered mainly in the densely constructed city areas having a high traffic volume.

Wind field changes i.e. the tendency towards strong turbulences as well as up and down winds can occur in the area of bigger buildings, the way they are present in construction topologies of heterogeneous, inner-city mixed development, large settlements and high rises as well as core area uses. With these changes there are, on one hand, positive effects like stronger turbulence of air-hygiene loads, on the other hand, there are also more and more restrictions in the wind comfort. On days with heat load, a cooling function originates from the water bodies in the urban area of Berlin for the nearby surroundings. They also act as air and ventilation pathways even under weather conditions with a strong exchange.

Noise protection devices are available at sections along the noise-emitting traffic paths and correspondingly sensitive uses. They are indicated primarily along the Federal Highway A 113 as well as along the rail tracks in the southern and western parts of the city. They represent an additional information in this map, because they cannot be taken into account explicitly in the modelling with respect to their possible influence on the spread of the air masses.

Areas not evaluated include water bodies, some places, tracks including the surrounding track bed.

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